Excerpt:
Sedna is the name given by astronomers for the newest planet to be discovered orbiting the Sun. Although the details of the size of the planet are still being sought, it is thought to be about 1300 miles in diameter and could be of a similar size to Pluto. Given the Pluto is generally accepted to be a planet in its own right, Sedna becomes the tenth planet to be found orbiting the Sun.
http://www.darkstar1.co.uk/sedna.htm